Heating system comprising at least two different radiations

ABSTRACT

The invention relates to a heating system used, for example, in applications such as the drying of paint. This heating system comprises a reflector ( 201, 505 ) having a concave section symmetrical with respect to an axis of symmetry ( 208, 508 ). It comprises in addition a first radiation system having at least a first radiation member ( 202, 501 ) capable of emitting a first type of radiation and a second radiation system having at least a second radiation member ( 203, 502 ) capable of emitting a second type of radiation. The second radiation system is positioned in a direction parallel to said axis of symmetry with respect to the first radiation system.

FIELD OF THE INVENTION

The invention relates to a heating system comprising at least tworadiation members capable of emitting at least two different types ofradiation.

The invention finds its application, for example, in a heating systemdesigned for industrial purposes such as curing of synthetic resins byheat, drying of paper, or baking of paints.

BACKGROUND OF THE INVENTION

U.S. Pat. No. 6,421,503 published Jul. 16, 2002 describes a heatingsystem comprising two radiation members capable of emitting twodifferent types of radiation. These radiation members are tubular inshape. The first radiation member comprises an incandescent filamentcapable of emitting a radiation in the near infrared range, whereas thesecond radiation member comprises a carbon ribbon capable of emitting aradiation in the medium infrared range.

It is a disadvantage of such a system that a given point of a coatingunder treatment is not simultaneously exposed to the two types ofradiation. FIG. 1 is a cross-sectional view of such a heating system andof a coating treated by this heating system. The heating system shown inFIG. 1 corresponds to a heating system of FIG. 5 from U.S. Pat. No.6,421,503. Such a heating system comprises a first radiation member 10comprising a first quartz envelope 12 and a carbon ribbon 14, and asecond radiation member 11 comprising a second quartz envelope 13 and anincandescent filament 15 kept in position by a support 15 a. The tworadiation members 10 and 11 are fixedly joined together by a centralsection 17. Each of the two radiation members 10 and 11 is covered witha reflecting layer 16 on an upper half of the respective quartz envelope12 or 13.

Under these operating conditions, the radiation emitted by the first andthe second radiation member 10 and 11 is necessarily downwardly directedwhen the heating system is arranged as shown in FIG. 1. Consequently, anobject 18 to be treated by this heating system is present below saidheating system. This object 18 comprises a coating 19 which is to betreated by the heating system. This may relate to, for example, a metalplate on which a paint comprising a pigment and a solvent has beendeposited.

In such a configuration, the rays emitted by the radiation members 10and 11 are not focused on the same location of the coating 19. As aresult, the overlap of the two types of radiation, which is particularlyadvantageous in applications such as the drying of paints, is limited,i.e. the spectral combination of the spectra of the two types ofradiation is limited.

In addition, the fact that the rays emitted by the radiation members 10and 11 are not focused on the same location of the coating 19 leads to aprolonged treatment time for the coating 19, since each point of thecoating 19 must be exposed to two types of radiation.

Another disadvantage of such a heating system is that the heating systemis cumbersome. An oven for drying the coating will in fact generallycomprise several heating systems arranged side by side, parallel to adirection in which the objects under treatment are moved. The dimensionsof the heating system of FIG. 1 are important in view of this direction,because the heating system comprises two radiation members 10 and 11arranged in this direction.

DESCRIPTION OF THE INVENTION

It is an object of the invention to provide a compact heating systemgiving an enhanced spectral combination.

To achieve this object, the invention provides a heating systemcomprising a reflector having a concave cross-section that issubstantially symmetrical with respect to an axis of symmetry, a firstradiation system comprising at least a first radiation member capable ofemitting a first type of radiation and a second radiation systemcomprising at least a second radiation member capable of emitting asecond type of radiation, said second radiation system being positionedin a direction substantially parallel to said axis of symmetry withrespect to said first radiation system.

According to the invention, the radiation systems are arranged in adirection parallel to the axis of symmetry of a cross-section of thereflector with respect to one another, and not in a directionperpendicular to the axis of symmetry of a cross-section of thereflector, as in the prior art. In this manner the rays emitted by thetwo radiation systems are focused for a major portion onto a same regionof the coating under treatment. The spectral combination of thedifferent emitted radiation types is enhanced thereby. In addition, theradiation systems are superimposed in the direction of emission of therays, which makes such a heating system compact.

Advantageously, the first radiation member comprises a first envelopeand further comprises a first reflecting layer deposited on a portion ofsaid first envelope. This renders it possible to improve the focusing ofthe radiation emitted by the first radiation member and accordingly toenhance the spectral combination of the emitted rays.

Advantageously, the second radiation member comprises a second envelopeand further comprises a second reflecting layer deposited on a portionof said second envelope. This renders it possible to improve thefocusing and to enhance the spectral combination of the emitted raysstill further.

Preferably, the first reflecting layer has a first concave section thatis substantially symmetrical with respect to a first axis of symmetryparallel to the axis of symmetry of the cross-section of the reflector,the second reflecting layer has a second concave section that issubstantially symmetrical with respect to a second axis of symmetryparallel to the axis of symmetry of the cross-section of the reflector,and the first and second reflecting layers have mutually opposeddirections of concavity and are adjacent to one another. Such aconfiguration renders possible in particular a thermal protection of theradiation members. Such a disposition of the reflecting layers rendersit possible to protect each radiation member from the radiation emittedby the other radiation member. Such a thermal protection renders itpossible to prolong the operational life of such a heating system.

Advantageously, the first radiation type is situated in the shortinfrared range, the second radiation type is situated in the mediuminfrared range, and the second radiation member is located between thereflector and the first radiation member. Such a configuration providesan even more enhanced spectral combination when these two types ofradiation are used in such a heating system.

In an advantageous embodiment of the invention, the reflector is a firstreflecting layer deposited on a portion of the envelope of the firstradiation member. This renders it possible in particular to omit the useof an external reflector, which reduces the bulk of such a heatingsystem.

Advantageously, the second radiation member comprises in addition asecond reflecting layer deposited on a portion of the envelope of thesecond radiation member. This renders it possible to improve thefocusing and to enhance the spectral combination of the emitted rays.

Preferably, the second reflecting layer has a concave section that issubstantially symmetrical with respect to an axis of symmetry parallelto the axis of symmetry of the cross-section of the first reflectinglayer, the first and second reflecting layers having mutually opposeddirections of concavity and being mutually adjacent. Such a heatingsystem provides in particular a thermal protection of the radiationmembers. Such a heating system is used by preference in combination withan external reflector, for example in an oven already fitted withreflectors. The heating system does not have an external reflector, sothat is not necessary to remove an external reflector if the heatingsystem is to be used in an oven fitted with a reflector.

Preferably, the reflecting layers used are ceramic layers. Suchreflecting layers provide a good focusing of the radiation, areresistant to high operating temperatures of such a heating system, formgood thermal protection means, and are easy to deposit on the radiationmembers.

Advantageously, the first and the second radiation member are kept inposition by at least one cap in which an end of the first radiationmember and an end of the second radiation member are inserted. It is notnecessary in this manner to interconnect the radiation memberspermanently as is the case in the prior art. This renders possible inparticular an easy exchange of one of the radiation members when it isdefective.

BRIEF DESCRIPTION OF THE FIGURES

The invention will be better understood and further details will becomeapparent from the following description which is given with reference tothe annexed drawings, which merely represent non-limitative examples andin which:

FIG. 1 is a cross-sectional view of a heating system from the prior art;

FIG. 2 a is a cross-sectional view of a first heating system accordingto the invention, and FIG. 2 b is a longitudinal sectional view of sucha system;

FIGS. 3 a and 3 b show a preferred embodiment of a heating systemaccording to the invention, in cross-section and in longitudinalsection, respectively;

FIG. 4 a is a cross-sectional view of a second heating system accordingto the invention, and FIG. 4 b is a longitudinal sectional view of sucha system; and

FIG. 5 a is a cross-sectional view of a heating system in anadvantageous embodiment of the invention, and FIG. 5 b is a longitudinalsectional view of such a system.

DETAILED DESCRIPTION OF AT LEAST ONE EMBODIMENT OF THE INVENTION

FIGS. 2 a and 2 b show a first heating system according to the inventionin cross-section and in longitudinal section, respectively. FIG. 2 bcorresponds to a section in a plane AA in FIG. 2 a. FIG. 2 a correspondsto a section in a plane BB in FIG. 2 b. Such a heating system comprisesan external reflector 201, a first radiation member 202 comprising anincandescent filament 204, a second radiation member 203 comprising astar-shaped filament 205, two supports 206, and two caps 207.

The first radiation member 202 in this example is a halogen tube capableof emitting in the short infrared range, denoted IR-A below, coveringmainly the wavelengths lying between 0.78 and 1.4 microns. A definitionof the wavelength has been given in 1987 by the InternationalElectrotechnical Commission (IEC) in section 845-01“Radiation,Quantities and Units”. Such a radiation member 202 in the form of ahalogen tube with an incandescent filament 204 is known to those skilledin the art. For example, applicant has made such a halogen tubecommercially available under reference 13402Z. The incandescent filament204 is supplied with current through external contacts 210 which areconnected to molybdenum foils 209, on which two ends of the incandescentfilament 204 are welded. The first radiation member 202 has an exhausttube tip 211 which results from the filling of the halogen tube with arare gas and halogen mixture during the manufacture of this tube.

The second radiation member 203 in this example is a halogen tubecapable of emitting in the medium infrared range, denoted IR-B,comprising mainly wavelengths lying between 1.4 and 3 microns. Such aradiation member 203 in the form of a halogen tube with a star-shapedfilament 205 is known to those skilled in the art. For example,applicant has made such a halogen tube commercially available underreference 17010Z, said tube being one from a range of lamps generallydenoted “High-Speed Medium Wave”. The second radiation member 203comprises external contacts 210, molybdenum foils 209, and an exhausttube tip 211, as does the first radiation member 202.

Alternative types of radiation members may obviously be used withoutdeparting from the scope of the invention. It is possible, for example,to use single-ended lamps, or also radiation members such as thosedescribed in U.S. Pat. No. 6,421,503.

The cross-section of the external reflector 201 shown in FIG. 2 a is aconcave section having an axis of symmetry 208. The first and the secondradiation member 202 and 203 are positioned in a direction parallel tosaid axis of symmetry 208 with respect to one another. In the exampleshown in FIG. 2 a, the axis of symmetry 208 of the external reflector201 is shown in vertical position, so that the first and secondradiation members 202 and 203 are positioned one above the other. Thispositioning causes the rays emitted by the first and the secondradiation member 202 and 203 to be mainly focused onto one and the sameregion centered on the axis of symmetry 208. A major spectralcombination is thus obtained at the level of said region. When an objectis thus treated by such a heating system, for example for drying a coatof paint, a point of the object under treatment is simultaneouslyexposed to the two types of radiation. As a result, the processing timeof the object is short, and the treatment is efficient. Furthermore,such a heating system is more compact than a heating system from theprior art, in which the radiation members are mutually positioned in adirection perpendicular to the axis of symmetry 208. This isparticularly advantageous because it is necessary in an oven comprisinga plurality of heating systems to reduce the space occupation in thedirection of movement of the objects under treatment, i.e. a directionperpendicular to the axis of symmetry 208.

It is important to note here that according to the invention theradiation members 202 and 203 are not necessarily positioned on the axisof symmetry 208. The radiation members 202 and 203 may be positionedwith respect to one another in a direction substantially parallel to theaxis of symmetry 208, i.e. in a direction enclosing a small angle withthe axis of symmetry, for example an angle smaller than 30°. In theexample of FIG. 2 a, the second radiation member 203 may thus beslightly shifted to the left or to the right with respect to theposition in which it is shown, without departing from the spirit of theinvention. In fact, such a slight shift will have little influence onthe spectral combination obtained in a region of an object undertreatment.

In the example of FIGS. 2 a and 2 b, the external reflector 201 has anelliptical shape, the first and the second radiation member 202 and 203being positioned around a focus of said ellipse. Such an ellipticalshape is particularly advantageous because it renders possible a goodfocusing of the rays emitted by the two radiation members 202 and 203.Moreover, the fact that radiation members of the halogen type are usedis particularly advantageous because the rays emitted by such radiationmembers can be easily focused.

In the example of FIGS. 2 a and 2 b, the second radiation member 203 ispositioned between the external reflector 201 and the first radiationmember 202. Applicant has found that a better spectral combination isobtained thereby than if the first radiation member 202 were positionedbetween the external reflector 201 and the second radiation member 203,in the case in which the first radiation member 202 emits in the shortinfrared range and the second radiation member 203 in the mediuminfrared range.

The first and second radiation members 202 and 203 in this example arekept in position with respect to one another by two caps 207 in whichthe ends of the radiation members 202 and 203 are inserted.Advantageously, these caps 207 are ceramic caps, and the ends of theradiation members 202 and 203 are joined to the respective caps by meansof cement. Obviously, alternative types of caps may be used, inparticular caps having reversible fixation means for the ends of theradiation members, for example by means of a rapid joint of the R7stype. This provides an easy replacement of one of the radiation memberswhen it is out of order. It is obviously possible to dispense with suchcaps, for example in that the radiation members 202 and 203 are joinedintegrally together by their central sections as described in U.S. Pat.No. 6,421,503. Such a solution, however, necessitates a delicate fusionstep and prevents the replacement of one of the radiation members whenit is defective.

In the example of FIGS. 2 a and 2 b, the first and the second radiationmember 202 and 203 are kept in position with respect to the externalreflector 201 by supports 206 which form part of said external reflector201. Alternative types of fixation may obviously be envisaged forkeeping the radiation members in position in the external reflector 201.It is to be noted that it is possible to dispense with the caps 207 orwith a central fusion section by inserting the ends of the two radiationmembers 202 and 203 into the supports 206, in which case the radiationmembers 202 and 203 are not one integral whole. The supports 206 thusserve to ensure the positioning of the radiation members with respect toone another and their positioning with respect to the external reflector201.

FIGS. 3 a and 3 b show a heating system in a preferred embodiment of theinvention in cross-section and in longitudinal section, respectively.This heating system comprises, in addition to the elements shown in FIG.1, a first reflecting layer 301 and a second reflecting layer 302. Thefirst and the second reflecting layer 301 and 302 have concave sectionswhich are symmetrical with respect to the axis of symmetry 208. Thefirst and the second reflecting layer 301 and 302 have mutually opposedconcavities and are adjacent. The first reflecting layer 301 in thisexample is deposited on an upper portion of the first radiation member202, and the second reflecting layer 302 is deposited on a lower portionof the second radiation member 203.

Such a heating system provides an improved focusing of the radiationemitted by the first and second radiation members 202 and 203, as wellas an enhanced energy efficacy as compared with the heating system ofFIGS. 2 a and 2 b. The radiation emitted in downward direction by thesecond radiation member 203 is in fact reflected by the secondreflecting layer 302 before it is reflected by the external reflector201 so as to reach an object under treatment arranged below the heatingsystem. The radiation emitted in upward direction by the first radiationmember 202 is directly reflected by the first reflecting layer 301 so asto reach the object under treatment. In this manner the major portion ofthe radiation emitted by the two radiation members 202 and 203 willreach the object under treatment and will be focused onto a region ofthe object, which region has a reduced surface area. The spectralcombination is thus enhanced in this region, as is indeed the powerlevel.

The reflecting layers used are known to those skilled in the art. Theymay be, for example, reflecting layers of gold. They may alternativelybe reflecting layers of a ceramic material. Such a reflecting layer ofceramic material is used in particular in a halogen lamp madecommercially available by applicant under reference 13185Z/98. It is tobe noted that the reflecting layers 301 and 302 are very thin inrelation to the thickness of the envelopes of the radiation members 202and 203. For example, the thickness of a reflecting layer is of theorder of 10 microns, whereas the thickness of the envelope of aradiation member is of the order of 1 mm. The thickness of thereflecting layers 301 and 302 in FIG. 3 a is purposely exaggerated sothat these two reflecting layers can be distinguished.

It is also to be noted that alternative configurations may be used inaccordance with the invention. For example, a heating system may have aceramic layer on only one of the radiation members, which provides animproved focusing, an improved spectral combination, and an improvedpower level compared with the heating system of FIGS. 2 a and 2 b.

In the example of FIGS. 3 a and 3 b, the reflecting layers 301 and 302are ceramic layers and are deposited such that they provide a thermalprotection for the radiation members 202 and 203. In fact, the radiationemitted by one of the radiation members will not reach the respectiveother radiation member directly, which leads to a lowering of thetemperature of the radiation members 202 and 203 compared with theheating system of FIGS. 2 a and 2 b. This leads to a prolonged usefullife of the radiation members 202 and 203.

In the example of FIGS. 3 a and 3 b, the external reflector 201 has twoelliptical parts. The first radiation member 202 is centered on thefocus of one of the two ellipses, the second radiation member 203 on thefocus of the other ellipse. Such an external reflector 201 isparticularly advantageous because it makes it possible to improve thefocusing of the rays emitted by the radiation members 202 and 203.

FIGS. 4 a and 4 b show a second heating system according to theinvention in cross-section and in longitudinal section, respectively.Such a heating system comprises, in addition to the elements shown inFIGS. 2 a, 2 b, 3 a, and 3 b above, a third radiation member 401. Thefirst radiation member 202 forms a first radiation system. The secondradiation member 203 and the third radiation member 401 form a secondradiation system. In this example, the second radiation system issituated below the first radiation system.

The invention is obviously not limited to these radiation systems. Forexample, the invention may comprise a first radiation system comprisingtwo radiation members and a second radiation system comprising tworadiation members.

In the example of FIGS. 4 a and 4 b, the third radiation member 401 is adischarge lamp capable of emitting in the ultraviolet range. The thirdradiation member 401 comprises two electrodes 402 and is covered with areflecting layer 403 on an upper portion of the envelope thatconstitutes the third radiation member 401. Such a third radiationmember 401 is known to those skilled in the art. For example, adischarge tube capable of emitting in the ultraviolet range is describedin U.S. Pat. No. 6,421,503.

Such a heating system renders it possible to obtain a wide spectrum ofwavelengths at the level of a region of an object under treatment. Itwill be noted, however, that it is possible to treat an object with onlyone or two types of radiation at a time with such a heating system. Itis possible, for example, to treat an object with a combination ofradiation in the short infrared and medium infrared ranges, while thethird radiation member 401 is not supplied with current. On the otherhand, it is possible to treat an object with exclusively a radiation inthe ultraviolet range. An advantage of such a heating system is that thesystem is compact and can be used in a large number of applications thatrequire various spectra of wavelengths.

It is also to be noted that it is possible to vary the spectra of theradiation of the first and second radiation members 202 and 203 independence on the desired application in that the supply voltages forthese radiation members are varied. This makes for an increase in thenumber of possible applications for such a heating system.

In the example of FIGS. 4 a and 4 b, the concave section of the externalreflector 201 is composed of segments. Such an external reflector iseasy to construct and renders it possible to obtain a good focusing ofthe radiation emitted by the two radiation systems.

If an external reflector of parabolic shape is used, such as theexternal reflector 201 of FIG. 2, it is advantageous to vary therespective positions of the radiation members 202, 203, and 401 as afunction of the desired application. For example, if a drying processthrough radiation of medium infrared is carried out, it is advantageousto place the second radiation member 203 around the focus of theexternal reflector, i.e. in the location of the first radiation member202. This may be effected in that the radiation members are rotated bymeans of, for example, a cap 207 capable of rotation with respect to theexternal reflector. The reflecting layers 301, 302, and 403 areadvantageously positioned at 120° with respect to one another in thiscase.

FIGS. 5 a and 5 b show a heating system in an advantageous embodiment ofthe invention in cross-section and in front elevation, respectively.This heating system comprises a first radiation member 501 comprising anincandescent filament 503 and a second radiation member 502 comprising astar-shaped filament 504. The first radiation member 501 comprises anenvelope of which a portion is covered with a reflecting layer 505. Thisreflecting layer 505 comprises a concave section which is symmetricalwith respect to an axis of symmetry 508. The radiation members 501 and502 have exhaust tube tips 507, molybdenum foils 509, and externalcontacts 510. The radiation members 501 and 502 are kept in positionwith respect to one another by means of caps 506 in which the ends ofthe radiation members are accommodated.

The reflecting layer 505 in such a heating system performs the functionof the external reflector 201 of FIGS. 2 a and 2 b. Such a heatingsystem is accordingly particularly advantageous, because it is lessbulky than the heating system of FIGS. 2 a and 2 b. Furthermore, such asystem may be used in an oven that is already provided with a reflector.

The heating system in this advantageous embodiment of the invention isnot limited to the individual embodiment shown in FIGS. 5 a and 5 b. Forexample, the second radiation member 502 may also comprise a reflectinglayer. The first radiation member 501, for example, may comprise areflecting layer on a lower half of its envelope, and the secondradiation member 502 may have a reflecting layer on an upper half of itsenvelope. Such a system will be used to advantage with an externalreflector such as the external reflector 201 of FIGS. 2 a and 2 b, butit may alternatively be autonomously used in an oven provided with, forexample, reflecting walls.

The verb “comprise” and its conjugations should be given a wideinterpretation, i.e. as not excluding the presence of elements otherthan those listed after said verb, and it is also possible for aplurality of elements to be present if listed after said verb andpreceded by the article “a” or “an”.

1. A heating system comprising a reflector (201, 505) having a concavecross-section that is substantially symmetrical with respect to an axisof symmetry (208, 508); a first radiation system comprising at least afirst radiation member (202, 501) capable of emitting a first type ofradiation; a second radiation system comprising at least a secondradiation member (203, 502) capable of emitting a second type ofradiation, said second radiation system being positioned in a directionsubstantially parallel to said axis of symmetry with respect to saidfirst radiation system.
 2. A heating system as claimed in claim 1,wherein said first radiation member comprises a first envelope andfurther comprises a first reflecting layer (301) deposited on a portionof said first envelope.
 3. A heating system as claimed in claim 2,wherein said second radiation member comprises a second envelope andfurther comprises a second reflecting layer (302) deposited on a portionof said second envelope.
 4. A heating system as claimed in claim 3,wherein said first reflecting layer has a first concave section that issubstantially symmetrical with respect to a first axis of symmetryparallel to the axis of symmetry of the cross-section of the reflector,said second reflecting layer has a second concave section that issubstantially symmetrical with respect to a second axis of symmetryparallel to the axis of symmetry of the cross-section of the reflector,and the first and the second reflecting layer have mutually opposeddirections of concavity and are adjacent to one another.
 5. A heatingsystem as claimed in claim 1, wherein the first radiation type issituated in the short infrared range and the second radiation type issituated in the medium infrared range.
 6. A heating system as claimed inclaim 5, wherein the second radiation member is located between thereflector and the first radiation member.
 7. A heating system as claimedin claim 1, wherein said first radiation member (501) comprises a firstenvelope, and the reflector (505) is a first reflecting layer depositedon a portion of said first envelope.
 8. A heating system as claimed inclaim 7, wherein said second radiation member (502) comprises a secondenvelope, and said second radiation member in addition comprises asecond reflecting layer deposited on a portion of said second envelope.9. A heating system as claimed in claim 8, wherein said secondreflecting layer has a concave section that is substantially symmetricalwith respect to an axis of symmetry parallel to the axis of symmetry ofthe cross-section of the first reflecting layer, the first and thesecond reflecting layer having mutually opposed directions of concavityand being mutually adjacent.
 10. A heating system as claimed in claim 2,wherein the reflecting layers used are ceramic layers.
 11. A heatingsystem as claimed in claim 1, wherein the first and the second radiationmember are kept in position by at least one cap (207, 506) in which anend of the first radiation member and an end of the second radiationmember are inserted.